1. Field of the Invention
The present invention is generally related to a combination dryer and blower appliance. More specifically, the present invention is related to control circuitry for controlling the electrical components of a dryer/blower.
2. Description of Related Art
There are many different types of hair dryers/blowers. For instance, typical hair dryers are shown in U.S. Pat. Nos. 4,195,217; 5,555,637; and 5,701,681. All of them, however, have AC cords attached and are not portable and self-contained. U.S. Pat. No. 6,449,870 entitled xe2x80x9cPortable Hair Dryerxe2x80x9d and by the inventor of the present invention discloses a portable dryer/blower appliance which uses an optional battery for its power supply.
Typically, prior art appliances of the type identified above have made use of a mechanical contact switch or switches for controlling the electrical power to the heating element(s) and blower motor. In general, these switches are fairly efficient as they do not generate any appreciable waste heat while conducting electricity. Any minimal waste heat that is generated by the switch while it is conducting is of such low intensity that it can easily be dissipated through the body of the dryer/blower without the need for extensively modifying the appliance, or even considering the switch heat in the initial design stages.
As mentioned, switches in prior art appliances typically consist of only the mechanical contact type due to several factors, the preeminent factor being the manufacturing costs associated with direct current (DC) operation. However, dryer/blower appliances have been recently introduced which use active devices for their switching capabilities, such as CMOS transistors and the like. Typically, this requires that the electrical power be converted from alternating current (AC) to DC, or alternatively, to elaborate mirror circuits for controlling the respective positive and negative portions of the AC power cycle.
Power transistors, unlike mechanical contact switches, can generate substantially more waste heat that must be dissipated (depending on the characteristics of the particular transistor type). Failure to properly channel the waste heat away from the device will often degrade its performance, making it less conductive, resulting in more waste heat which is not channeled away from the device, more inefficiency, and eventually causing the device to fail due to overheating (this is referred to as the xe2x80x9cheat avalanche effectxe2x80x9d). Additionally, certain semiconductor switching devices generate proportionally more heat as a result of changing states from insulator to conductor than from conducting electricity alone. Therefore, again depending on the characteristics of the individual transistor type selected for use, pulsing circuits using these devices potentially generate even more waste heat than devices employed for merely switching the electrical power to the electrical components of the dryer/blower xe2x80x9conxe2x80x9d and xe2x80x9coff.xe2x80x9d
The present invention relates to a blower dryer appliance typically used for drying and styling hair. When electrically activated, these appliances virtually always route electrical power to the fan or blower motor prior to or simultaneously with the heating element(s). Semiconducting switching devices are used for regulating, controlling and/or switching electrical power generated from waste heat that must be dissipated. Typically, heat is conducted and/or channeled away from the semiconducting switching device through a heat sink which is thermodynamically and mechanically coupled to the device. The greater the coverage area of the heat sink, the more waste heat can be dissipated depending on the ability of the heat sink to make contact with cooler, ambient air. This adds costs to the dryer/blower for engineering the heat sink, cost of the sink itself, and necessary design changes dryer/blower for accommodating the sink. The presently disclosed invention utilizes the inherent characteristics of the dryer/blower for channeling and reusing waste heat generated from an active switching device by positioning the active device in the air path of the blower. Relocating the heat generation portion of the control circuitry to the air path has three major benefits: greater cooling effect for the switching transistor and therefore more efficient transistor conduction and switching operation; utilizing smaller and less costly heat sinks; and the cumulative effect of combining the waste heat generated by the switch to the intentional heat effect generated by the heating element(s).